Method of preparation of carbides



Patented Aug. 30, 1932 UNITED STATES PATENT OFFICE ROYAL L. SESSIONS, OFYORK, PENNSYLVANIA, ASSIGNOR, BY MESNE ASSIGNMENTS, TO MOLYBDENUMCORPORATION OF AMERICA, 01: NEW YORK, N. Y., A CORPORATION or DELAWARENo Drawing.

The present invention relates to the preparation of carbides of metalsof the sixth in making toolsand dies. These products are produced bymixing, pressing and sintermg the powdered carbide and the powderedmetal. The auxiliary metal acts as a cementing agent to support and holdthe carbide which, while very hard, is brittle, and alone hasinsuflicient structural strength. The methods heretofore practiced inthe preparation of these products have required the comminution of theingredients to as small a size as possible by mechanical means and theintimate mechanical mixing by grinding of these ingredients.

Cobalt-tungsten carbide has been prepared in accordance with U. S.Patent 1,549,615, British Patent 213,524, and German Patent 420,689, allof which discuss the making of a hard alloy of cobalt, nickel or ironwith tungsten carbide (having up to 10% binder such as cobalt, 3% to 10%carbon with the remainder tungsten), and the use of such for wiredrawing dies. British. Patent 251,- 929 and German Patent 434,527discuss the use of such tungsten carbide for making cutting and grindingtools containing 10% to 20% of auxiliary metal such as cobalt, with 3%to 10% carbon, thebalance being tungsten. It thus appears thatcobaltnickeland iron-tungsten carbide, having up to 20% binder and from3% to 10% carbon have valuable properties in the manufacture of tools ofvarlous sorts.

In tools and dies made according to the methods now available, thequality of the product is dependent to a large extent on the employmentof very small particles of binder such as cobalt metal powder and car-..METHOD OF PREPARATION OF CARBIDES Application filed October 9, 1928.Seria No. 311,408.

bide such as tungsten carbide, which must be intimately mixed so thatthe carbide will have been wetted by the binder. Not only must theseingredients be present in condition to be in intimate contact, but itappears that the metal powder used as a binder and the carbide should befree of deleterious foreign substances.

Briefly the preparation of tungsten carbide as heretofore practiced,consists in making pure tungstic oxide, the hydrogen or carbon reductionof the same, and subsequent carburization of the tungsten metal powderproduced. Each one of these steps is expensive and the carbide requiresgrinding to produce small particle size. As regards cobalt metal powder.there are t arious steps, such as the manufacturing of the oxideofcobalt and the reduction of the same with hydrogen or any othersuitable means. The cobalt metal powder is also ground to produce smallparticle size. The metallic cobalt powder and tungsten carbide are mixedin the correct proportions and ground very intimately. This grinding maybe performed in a ball mill, and the mixed powders are screened throughan exceedingly fine sieve. These grinding operations both for particlesize and mixing are diificult to control, resulting in lack ofuniformity and uncertainty of product, and contamination, especially onaccount of the abrasive action of tungsten carbide. This material ispacked into a form under pressure and sintered. a for instance bypassing electricity through it.

It is possible to make a series of hard alloys from the various abovementioned carbm'ized metals and binders having varying degrees ofhardness and other valuable properties. As an example of the practicalapplication of the invention, I will, however, discuss the same moreparticularly with respect to the preparation and properties of tungstencarbidecobalt compositions which may, for convenierce, be designated ascobalt-tungs en car- -According to the present invention, however, theintimate mixing of the binder with the carbide and the obtaining of verysmall particles of carbide and binder or auxlhary mate mixing. In thismanner one is enabled to obtain the resulting product having thenecessarily small particle size and intimate mixture without mechanicaloperations such as grinding.

According to the preferable method of operation, the preparation of thecobalt tungsten carbide is based on the employment of a 15 B. solutionof ammonium tungs compound containing both cobalt and tungsten, such asnormal cobalt tungstate or cobalt para tungstate, or a mixture of thetwo. These compounds have definite and well known compositions. As theseare chemical compounds rather than mixtures, the ratio of cobalt andtungsten is definite and not changeable and one has an accuratefoundation for all calculations.

In making normal cobalt tungstate one may take a 15 B. ammoniumtungstate solution, which will contain approximately .12 g. of W0 percc. and add thereto the calculated amount -of soluble cobalt (such ascobalt chloride, cobalt nitrate, etc.) to form normal cobalt tungstate.The precipitate formed should be washed and dried. To make cobalt paratungstate, one may take a tate and before adding the soluble cobaltsolution, sufficient hydrochloric acid is added at room temperature toproduce a solution of ammonium para tungstate. At this point the cobaltchloride solution is added, which throws down a peach coloredprecipitate of cobalt para tungstate. In this form it can be washed anddried and is thereafter ready for reduction to cobalt-tungsten carbide.

In reducing normal cobalt tungstate, one may take about five to sevenparts of the dehydrated powder as indicated above, and mix the sameintimately with about one part of carbon in any suitable form. The mixis placed in a graphite crucible or other suitable container. It isconvenient to place a graphite disc over the mix and loose lampblack maybe used to cover the disc to prevent oxidation. The crucible is placedin a 'furnace gradually heated for a period of three hours to bring itto a temperature of about 1,000 (3., at which it is held for about fivehours. The duration of heating will depend very largely on thedimensions of the crucible or other container, and the quantity oftungstate treated. Less carbon will be required where a stronglyreducing atmos-' phere is maintained in the furnace. Substantially thesame procedure may be folaeraeer lowed in reducing cobalt paratungstate. A reducing and carbonizing gas may be used in place 01' thesolid carbon.

I prefer a minimum temperature to pre-.

vent undue sintering. It is, however, possible to employ highertemperatures'as long as the cobalt does not become too fluid or thedecomposition point of the carbide is not reached. 7

In carrying out these reducing and concurrent carburization operations,all the carbon apparently unites with the tungsten, forming a tungstencarbide, the cobalt being reduced to the metallic state to provide material for a matrixor binder. This process may be described as aselective carburization, proceeding concurrently with the reduction. Itis probable that the matrix forming material thus formed consists of apredominant amount of pure cobalt possibly admixed with varying amountsof tungsten or tungsten and carbon. The amount of carbon used in thereduction of cobalt tungstate is based on the supposition that thetungsten content of the cobalt tungstate is converted to tungstenmonocarbide. If the normal and para tungstates are merely dried and notcompletely dehydrated before reduction, less carbon should be used.

Tungsten forms definite compounds with carbon known as tungstenmonocarbide and ditungsten carbide having 6.12% and 3.16%, V

- The cobalt-tungsten carbides thus pro- I duced are in the form ofpulverant powders of exceedingly smfl particle size. This isthe resultof employing combined cobalt and combined tungsten in the state ofmolecular subdivision instead of the metallic state. If the optimumtemperature has been exceeded, the cobalt-tungsten carbide may besintered. When normal cobalt tungstate is used as a basic material,there will be 24.2 parts of cobalt to 75.8 parts of timgsten, whiletheproduct made from cobalt para tungstate will have 12.1 parts cobalt to87.9 parts tungsten.

If the desired ratio of cobalt and tungsten in the tool forming materialabove referred to is 15 cobalt to 80 tungsten, it will be noted thatthis percentage is intermediate between the percentages obtained whenusing pure cobalt tungstate and pure cobalt para tungstate. In order toobtain this desired perpara tungstate powders may be mixed in thedesired proportions which are about 31 parts normal to 100 parts of paratungstate whereupon the cobalt-tungsten carbide obtained by thereduction and concurrent carburiza- E0111 will have the desiredpercentage of co- This process obviates the necessity of making cobaltoxide and the reduction of the same to cobalt metal powder. It alsoobviates the necessity of making tungstic acid, the reduction of thesameto tungsten metal powder and the carburization of the metal totungsten carbide. In place of these operations in connection with themanufacture of cobalt metal powder and tungsten carbide, this processcalls for a single precipitation of cobalt tungstate, the precipitatebeing easily washed. No amount of mechanical mixing and grinding ofcobalt metal powder and tungsten carbide can give the degree of intimacywhich is consequent upon the use of cobalt tungstates.

The cobalt-tungsten carbide as prepared is a powder. The particle sizeis exceedingly small and when the powder is placed in a form andsintered, one obtains a tool having vastly improved properties overtools made from the mechanically produced mixture of cobalt and tungstencarbide. There is, a noticeable improvement, especially with respect tothe toughness of the tool and its resistance to shock.

As a possible variation of the process above, cobalt oxide and ammoniumpara tungstate or tungs-tic acid (HJVOQ or tungsten oxide (VVO incorrect proportions can be intimately ground with carbon and the chargereduced in the same manner as cobalt tungstate. This grinding operationis much less diificult than the grinding necessary where cobalt metalpowder and tungsten carbide are employed as raw materials. In casesufiicient carbon has been used, the extra carbon of the mix willcombine with the reduced tungsten as explained in reducing cobalttungstate to form tungsten carbide. This process is superior to theprocess of preparing separately cobalt metal powder and tungsten carbidebecause some of the necessary operations are obviated by the singlereduction of the cobalt and tungsten with the concurrent carburizationof the tungsten. It, however, produces the fine particle size as boththe cobalt and tungsten were in the state of molecular subdivision.

Inasmuch as 12.1% is the lowest percentage of cobalt to be had from theuse of normal cobalt tungstate alone, and certain tools, such as wiredrawing dies may employ much lower cobalt content and higher tungstencarbide content, one may obtain such alloys y using the cobalt oxide andtungsten compound mixture, or may dilute the cobalt para tungstate withtungsten as an acid or oxide.

()n the other hand, when one desires to exceed the highest percentage(24.2) of cobalt, in the cobalt tungsten carbide, it is possible toemploy additional cobalt oxide, or hydrate.

I desire it to be understood that the term cobalt-tungstate when usedwithout qualification is to include normal cobalt tungstate, cobaltparatungstate, or any other cobalt tungstate or mixtures of the varioustungstates of cobalt.

I have described the preparation of cobalttungsten carbide inconsiderable detail. The methods employed in making nickel-tungstencarbide, cobalt-molybdenum carbide,

nickel-molybdenum carbide, cobalt-chromium carbide, and nickel-chromiumcarbide, or mixtures of any of these products will, in general, followthe same procedure with such variations in percentages, temperatures andperiods of heating as the particular conditions require.

When carbon is used as a reducing agent the auxiliary metal and carbideforming metal are reduced and the latter metal concurrently carburize'din the manner above set forth.

Where the metallic constituents are combined with volatile constituentssuch as oxygen and ammonia, these elements escape during reduction.Where, however, the metallic constituents are combined with non-volatileelements, one should select such raw materials that the foreign matterpresent in the reduced and carburized product may remain withoutmaterially afi'ecting the properties, or may be separated from thiscobalt-tungsten carbide by some process which will not decompose thecobalt-tungsten carbide.

I claim:

1. The method 'of making a carbide composition having at least twometallic constituents, at least one of which forms a carbide whileanother constituent does not readily form a carbide, which consists inbringing about a close association of all said constituents while in thechemically combined condition, and concurrently effecting a reduction ofboth constituents and a selective carburization of one of theconstituents by car bon, and without fusion or sintering.

2. The method of makin a carbide composition having two meta licconstituents with only one of which carbon readily forms a carbide,which consists in bringing about a close association of bothconstituents while each of them is in chemically combined condition, andconcurrently effecting a reduction of both constituents and a selectivecarburization of one of the constituents by carbon, and without fusionor sintering.

3. The method of making a carbide composition having two metallicconstituents with only one of which carbon readily forms a carbide,which consists in concurrently recontaining both of these metalscombined with elements such that the carbide alloy may be separatedtherefrom the reduction and carburization being carried on attemperatures insuflicient to cause fusion.

4. The method of making a carbide composition having two metallicconstituents with only one of which carbon readily forms a carbide,which consists in concurrently reducing and selectively carburizing amixture containing both of these metals combined with volatileconstituents the reduction and carburization being carried on attemperatures' insuflicient to cause fusion.

5. The method ofmaking a carbide composition having two metallicconstituents with only one of which carbon readily forms a carbide,which consists in reducing and carburizing a chemical compound includingboth of said constituents at temperatures insuffcient to cause fusion.

6. The method-of preparing a carbide composition containing at least twometallic constituents, at least one of which forms a car bide, whileanother constituent does not read ily form a carbide, said alloy havinga predetermined relative amount of said two constituents, which consistsin preparing a chemical compound including said two constituents, mixingwith said compound a compound containing one of said constituentscombined with a removable component, and reducing and carburizing themixture at temperatures insuflicient to cause fusion.

7. The method of making a carbide com-- position having at least twometallic constituents, at least one of which forms a carbide whileanother constituent does not readily form a carbide, which consists inbringingabout a close association of all said constituents, while in thechemically combined condition, with carbon, and reducing the mixture ata temperature at which the noncarburizable metal is converted to themetallic state and the other metal is concurrently reduced andcarburized, the temperatures beand cobalt para tungstate at temperaturesinsufiicient to cause fusion.

11. The method of making cobalt-tungsten carbide which consists inreducing and carburizing cobalt tungstate at' temperatures insuflicientto cause fusion.

12. The method of making cobalt-tungsten carbide which consists inreducing and carburizing cobalt para tungstate at temperaturesinsufiicient to cause fusion;

13. The method of making cobalt-tungsten carbide which consists inreducing and carburizing normal cobalt tungstate at temperaturesinsuflicient to cause fusion.

14. The method of making cobalt-tungsten carbide which consists inbringing about an intimate association of cobalt and tungsten when bothare in the chemically combined condition and effecting a simultaneousreduc; tion of both materials and concurrently and selectivelycarburizing the same without fusion or sintering.

15. The method of making cobalt-tungsten carbide which consists inpreparing a mix-.

ture of normal cobalt tungstate and cobalt para tungstate, mixing thesame with carbon and reducing the mixture at a tempertaure suflicient toconvert the cobalt to metal and concurrently carburize the tungsten butinsufiicient to cause fusion.

16. The method of making cobalt-tungsten carbide which consists inmixing cobalt tung state with carbon and'reducing the mixture at atemperature suflicient to convert the cobalt to metal and concurrentlycarburize the tungsten but insufiicient tocause fusion. 7

. 17 The method of preparing cobalt-tungsten carbide having apredetermined percentage composition of cobalt and tungsten difi'eringfrom the relative amounts of cobalt and tungsten present in a tungstateof cobalt,

which consists in mixing with a selected tungstate of cobalt a compoundcontaining at least one of said metals combined with a removablecomponent, and reducing and concurrently carburizing the mixture.

18. The method of producing a cobalttungsten carbide of a desiredrelative propor tion of cobalt and tungsten which consists in mixingtogether two cobalt tungstates, one having less than the desiredpercentage of cobalt While the other has more than the desiredpercentage of cobalt, to produce a physical mixture having anintermediate composition with the desired relative proportion of cobaltand tungsten, and reducing and carburizing the mixture.

19. The method of making cobalt-tungsten carbide which consists inmixing dehydrated fate such cobalt tungstate, drying the precipitate andmixing it with carbon. and heating the mixture at a temperaturesuflicient to re duce and concurrently carburize the same and 5 producemetallic cobalt and tungsten carbide and insuflicient to decompose saidcarbide or cause fusion.

Signed at York, in the county of York and State of Pennsylvania, this4th day of October,1928.

ROYAL L. SESSIONS.

